This invention relates to stiffening a composite material web structure with transverse stiffeners. In the conventional, aluminum-metal design approach, a standard angle stiffener is utilized which is riveted against the web. However, fastening methods utilizing rivets cannot be used in graphite epoxy parts because the expansion of the head may crack the resin. Furthermore, fasteners should be electro-chemically compatible to prevent corrosion. The solution of utilizing screw type fasteners becomes highly uneconomical and utilizing so-called stiffeners becomes complicated in design, tooling and manufacture. By the teachings of this invention, transverse web stiffeners are utilized in the form of tubular elements having flattened ends which are inserted between the composite laminations of the web material.
The following references were found to be of interest: U.S. Pat. Nos. 3,831,333; 3,995,080; 4,047,354; 4,113,910; 4,129,974; 4,198,018; 4,219,980; and 4,219,980; Italian Pat. No. 682,106 and British Pat. No. 640,341.
A close approach to the present inventive method and proposed construction was not observed and accordingly, the patents should be considered as being of general interest and illustrating the scope of the available art. Several of these patents disclose various types of transverse stiffeners or reinforcements for beam structures of the general type under consideration, however, none appear to be close structurally to the proposed concept.